Combination touch and transducer input system and method

ABSTRACT

A combination touch and transducer input system is provided, which facilitates user input into an electronic system with a finger and/or a transducer (e.g., a stylus). The system includes a transducer configured to generate an electric field, and a sensor including an array of electrodes and a controller. The transducer is configured to transmit digital data, such as pen pressure data and switch status data, to the sensor. For example, the transducer comprises electronic circuitry configured to encode the digital data in a signal for transmission to the sensor. The sensor controller is configured to operate both in a touch sensing mode and in a transducer sensing mode. During the touch sensing mode, the controller determines a position of a proximate object (e.g., a finger) by capacitively sensing the object with the array of electrodes. During the transducer sensing mode, the controller determines a position of the transducer based on a signal received by the array of electrodes from the transducer, and also receives and decodes the digital data encoded in the received signal. Digital data can be encoded in a signal using any suitable digital modulation techniques, such as a Frequency-Shift Keying (FSK) technique.

BACKGROUND Field of the Invention

The present invention generally relates to user interfaces for electricdevices, and more specifically relates to touch sensors and digitizersystems.

Description of the Related Art

A variety of different types of input devices are commonly used in avariety of different electronic systems, including computers (e.g.,laptop computers, tablet computers, personal digital assistants) andcommunication devices (e.g., mobile phones, wireless handheldcommunication devices). One type of input device is generally referredto as a touch sensor or proximity sensor. A touch sensor uses a varietyof different techniques to determine the position of proximate objects,such as fingers. For example, capacitive touch sensors determine theposition of proximate objects by determining a change in capacitancethat occurs due to the presence of proximate objects. Another type ofinput device is commonly referred to as a digitizer tablet, but alsoreferred to as a graphics tablet, graphics pad, or drawing tablet.Digitizer tablets include a sensing surface upon which a user can enterinput using a transducer, typically implemented as a stylus or otherpen-like drawing apparatus. In typical digitizers, the transducer emitsan electromagnetic signal, which is detected by the sensing surface. Theelectromagnetic signal detected by the sensing surface is then used andprocessed to determine the position of the transducer.

In general, digitizers offer increased position-detection accuracy andresolution when compared to typical touch sensors. Digitizers typicallyrequire the use of a specialized transducer for inputting. It has beendesirable to combine the attributes (e.g., convenience) of touch sensorswith the improved accuracy and resolution of digitizers. Unfortunately,combination touch sensor-digitizers have had limited applicability,mainly due to high cost and complexity associated with implementation,the additional three-dimensional space required to accommodate thecombination, and the requirement for special types of displays thatcould support both touch sensing and transducer (e.g., stylus) sensing.Thus, there remains a continuing need for improved combination touchsensor and transducer-based input devices.

BRIEF SUMMARY

This summary is provided to introduce a selection of concepts in asimplified form that is further described below in the DetailedDescription. This summary is not intended to identify key features ofthe claimed subject matter nor is it intended to be used as an aid indetermining the scope of the claimed subject matter.

The embodiments of the invention provide systems and methods forfacilitating user input into an electronic system. Combination touch andtransducer input systems are provided, which facilitate user input bothwith ordinary objects (e.g., fingers) and with transducers that emit anelectric field for position detection.

According to one aspect of the invention, a combination touch andtransducer input system is provided, which includes a transducer (e.g.,a stylus), an array of electrodes, and a controller coupled to the arrayof electrodes. The array of electrodes and the controller together forma sensor that is used for detecting both the position of a proximateobject, such as a finger, and the position of the transducer. Thetransducer is typically in the form of a stylus or other pen-likeapparatus, and is configured to generate an electric field. Thecontroller of the sensor is configured to operate in a proximate objectsensing mode (hereinafter the “touch mode”) and in a transducer sensingmode (hereinafter the “transducer mode”), either simultaneously or in analternating manner by switching between the two modes in successivesampling periods.

When operating in the touch mode, the controller determines theposition(s) of one or more proximate objects (e.g., fingers) bycapacitively sensing the object(s) with the array of electrodes. In oneexample, the controller determines the position of each object bydetecting a change in capacitance caused by that object in the array ofelectrodes. When operating in the transducer mode, the controllerdetermines a position of the transducer by measuring attributes (e.g.,amplitudes, phases, etc.) of a plurality of sensing signals that areinduced in the array of electrodes by the electric field generated bythe transducer. Specifically, as the transducer (an antenna) and each ofthe array of electrodes are capacitively coupled, the controllerdetermines the position of the transducer by measuring a charge inducedat each of the array of electrodes.

The transducer is further configured to send digital data to the sensor.For example, the transducer may include electronic circuitry (e.g., amicrocontroller unit (MCU) or microprocessor) configured to encodedigital data in the electric field for transmission to the array ofelectrodes, and the controller of the sensor is configured to decode thedigital data received by the array of electrodes. For example, thedigital data may include data related to the transducer's pen tippressure, the transducer's switch status, or the transducer's unique ID.

According to another aspect of the invention, the transducer isconfigured to selectively generate an electric field at multiplefrequencies and to encode digital data in frequency shifts of thegenerated electric field, while the controller is configured to detectthe plurality of sensing signals at multiple frequencies and to decodethe digital data encoded in the frequency shifts. The multiplefrequencies may be determined, for example, by dividing down a basefrequency, so as to avoid harmonics generated by any signal transmittedby the transducer. Any suitable Frequency-Shift Keying (FSK) technique,including the Manchester coding scheme, may be used to encode digitaldata. According to a further aspect of the invention, any other digitalmodulation technique may be used to encode digital data, includingAmplitude-Shift Keying (ASK) technique, Phase-Shift Keying (PSK)technique, and Quadrature Amplitude Modulation (QAM) technique.

In accordance with another aspect of the invention, the digital datatransmission may be bi-directional. That is, in addition to thetransducer transmitting digital data to the controller, the controllermay be configured to transmit digital data to the transducer.

According to one aspect of the invention, the transducer and thecontroller communicate asynchronously.

According to one aspect of the invention, the transducer is configuredto selectively generate the electric field at multiple frequencies andthe controller is further configured to select one (or more) of themultiple frequency channels as receiving channel(s). For example, thecontroller may determine a signal-to-noise ratio for each frequencychannel and select the frequency channel having the highestsignal-to-noise ratio as the receiving channel. According to a furtheraspect of the invention, when two or more combination touch andtransducer input systems are provided, the transducer of the firstsystem is configured to generate the electric field at a first frequency(or a first set of frequencies) and the transducer of the second systemis configured to generate the electric field at a second frequency (or asecond set of frequencies) different from the first frequency (or thefirst set of frequencies), to avoid cross-coupling between the twosystems that may be used proximate to each other.

According to one aspect of the invention, the array of electrodesincludes a first set of elongate electrodes arranged substantially inparallel with each other and extending in a first direction and a secondset of elongate electrodes arranged substantially in parallel with eachother and extending in a second direction that is different from thefirst direction. For example, the first and second directions may begenerally perpendicular to each other. Each pair of at least one of thefirst set of elongate electrodes and at least one of the second set ofelongate electrodes forms a capacitor. When operating in the touch mode,the controller is configured to supply a signal to each of the first setof elongate electrodes, detect a capacitance change reflected in asignal outputted from each of the second set of elongate electrodes, anddetermine the position of the proximate object based on the detectedcapacitance change.

When operating in the transducer mode using the electric field coupling,the controller is configured to measure attributes (e.g., amplitudes andphases) of a plurality of sensing signals outputted from both the firstand second sets of elongate electrodes and calculate the position of thetransducer based on the measured attributes. According to a furtheraspect of the invention, when operating in the transducer mode, thecontroller is configured to measure an attribute of a sensing signaloutputted from each of the first or second set of elongate electrodeswhile selectively terminating (e.g., floating, terminating via aresistor to ground, or grounding) two or more of the first or second setof elongate electrodes that are adjacent to that elongate electrodebeing sensed, to thereby improve the quality of the sensing signal.

According to one aspect of the invention, the controller is configuredto alternate between operating in the touch mode and operating in thetransducer mode in successive sampling periods of the system. Accordingto another aspect of the invention, the operating mode may be selectedby a user of the system. According to a further aspect of the invention,the controller is configured to selectively divide the array ofelectrodes into a touch mode section and a transducer mode section, andto simultaneously operate in the touch mode in the touch mode sectionand in the transducer mode in the transducer mode section. The touchmode section may consist of a plurality of touch mode sub-sections,while the transducer mode section may consist of a plurality oftransducer mode sub-sections. According to a still further aspect of theinvention, the controller periodically switches the touch mode sectionand the transducer mode section such that a given point on the array ofelectrodes alternates between being in the touch mode section and beingin the transducer mode section.

According to one aspect of the invention, the controller includes acascoded transimpedance amplifier coupled to the array of electrodes.The cascoded transimpedance amplifier is configured to amplify theplurality of sensing signals induced by the electric field in the arrayof electrodes, while advantageously isolating the input capacitance ofthe array of electrodes from the feedback resistor of the transimpedanceamplifier.

According to one aspect of the invention, the transducer includes acapacitor or a battery that is configured to function as a power supplyfor the transducer.

According to a further aspect of the invention, the controller isconfigured to determine the position of the transducer by fitting themeasured attributes (e.g., amplitudes, phases, etc.) of the plurality ofsensing signals to a pre-determined parameterized curve. According toone aspect of the invention, the pre-determined parameterized curverelates a plurality of positions of the transducer relative to oneelectrode with a plurality of attributes of sensing signals induced inthat electrode by the transducer at the plurality of positions,respectively. According to one aspect of the invention, thepre-determined parameterized curve is empirically derived for use withthe transducer having a particular tip shape and the array of electrodeshaving a particular electrode configuration pattern. According to oneaspect of the invention, the pre-determined parameterized curve includesa position parameter and at least one or more of a height parameter anda tilt parameter. According to one aspect of the invention, the systemfurther comprises an external processor, such as a processor in a hostsystem (e.g., a PC that includes the combination touch and transducerinput system), and the controller and the external processor perform thecurve fitting operation, which may be computationally intensive, indistributed processing.

According to another aspect of the invention, a cordless transducer isprovided, which is configured for use with an array of electrodes,wherein the cordless transducer and the array of electrodes arecapacitively coupled. The cordless transducer includes a pen-shapedhousing including a pen tip at its distal end, and a transducercontroller arranged within the pen-shaped housing. The transducercontroller controls the operation of the cordless transducer, andincludes a pressure sensor for detecting the pressure applied to the pentip. The cordless transducer also includes an antenna coupled to thetransducer controller to transmit the pressure sensor data, which isdetected by the pressure sensor, as digital data to the array ofelectrodes. The transducer controller includes a power storage device,such as a battery or a capacitor, which supplies power to drive thetransducer controller, to thereby achieve the cordless transducer.

According to another aspect of the invention, a combination touch andtransducer input system is provided, which includes a cordlesstransducer described above, and a sensor. The sensor includes an arrayof electrodes and a sensor controller coupled to the array ofelectrodes. The sensor controller is configured to operate in both atouch mode to determine a position of a proximate object by capacitivelysensing the object with the array of electrodes, and in a transducermode to determine a position of the cordless transducer by measuringattributes of a plurality of sensing signals induced in the array ofelectrodes by the electric field generated by the cordless transducer.The cordless transducer transmits pressure sensor data as digital datato the sensor.

According to a further aspect of the invention, a method is provided forselectively determining a position of a proximate object and a positionof a transducer. The method includes eight steps. First, a proximateobject is capacitively sensed with an array of electrodes. Second, aposition of the proximate object is determined based on the capacitivesensing. Third, an electric field is generated with the transducer.Fourth, digital data is transmitted from the transducer. Fifth, aplurality of sensing signals are induced based on the electric field ina corresponding plurality of electrodes in the array of electrodes.Sixth, attributes of the plurality of sensing signals are measured.Seventh, a position of the transducer is determined based on themeasured attributes of the plurality of sensing signals. Eighth, thedigital data is received with the array of electrodes.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The present invention may more readily be understood by reference to theaccompanying drawings in which:

FIG. 1 shows a tablet computer, which includes a combination touch andtransducer input system in accordance with an embodiment of theinvention;

FIG. 2 is schematic representation of a sensor for use in a combinationtouch and transducer input system, the sensor including a controller andan array of electrodes, in accordance with an embodiment of theinvention;

FIGS. 3A and 3B are schematic representations of a transducer for use ina combination touch and transducer input system, in accordance with anembodiment of the invention;

FIG. 4 is a block diagram of a transducer in accordance with anembodiment of the invention;

FIG. 5A is a block diagram of a sensor, including a controller and anarray of electrodes, in accordance with an embodiment of the invention;

FIG. 5B is a schematic representation of an array of electrodes that isdivided into one or more touch mode sections and one or more transducermode sections, according to one embodiment of the invention;

FIG. 6 is a block diagram of a processing stage, which may be includedin the controller of FIG. 5A, in accordance with an embodiment of theinvention;

FIG. 7 is a circuit representation of a charge amplifier, which may beincluded in the processing stage of FIG. 6 , in accordance with anembodiment of the invention;

FIG. 8 is a circuit representation of a voltage amplifier, which may beincluded in the processing stage of FIG. 6 , in accordance with anembodiment of the invention;

FIG. 9 is a circuit representation of a transimpedance amplifier, whichmay be included in the processing stage of FIG. 6 , in accordance withan embodiment of the invention;

FIG. 10 is a circuit representation of a cascoded transimpedanceamplifier, which may be included in the processing stage of FIG. 6 , inaccordance with an embodiment of the invention;

FIG. 11A is a flow chart illustrating a process of scanning an array ofelectrodes during a transducer mode, according to one embodiment of theinvention;

FIGS. 11B and 11C each illustrate an array of electrodes, in which whenone elongate electrode is sensed during a transducer mode using theelectric field coupling, two or more of the elongate electrodes adjacentto the electrode being sensed are selectively terminated (e.g., floated,terminated via a resistor to ground, or grounded) according to oneembodiment of the invention;

FIG. 11D illustrates an array of electrodes suitably arranged to pick upa magnetic field component of an electromagnetic field generated by atransducer, during the transducer mode, in accordance with oneembodiment of the present invention;

FIG. 12 is a schematic representation of a digital filtering procedureaccording to one embodiment of the invention;

FIG. 13A is a flow chart illustrating a sample process used to determinea position of a transducer based on a curve-fitting technique, accordingto one embodiment of the invention;

FIG. 13B is a sample parameterized curve that is empirically derived andused to determine the position of a transducer, according to oneembodiment of the invention;

FIG. 13C is a sample phase locked loop (PLL) circuit suitable forgenerating multiple frequencies for use in accordance with oneembodiment of the invention;

FIG. 14 shows a sample data frame used to transmit digital data betweena transducer and a sensor in a combination touch and transducer inputsystem, according to one embodiment of the invention;

FIG. 15 is a flow chart illustrating a process performed by atransducer, including the process of encoding and transmitting digitaldata to a sensor, according to one embodiment of the invention; and

FIG. 16 is a flow chart illustrating a process of decoding digital dataencoded in frequency shifts of a signal generated by a transducer,according to one embodiment of the invention.

DETAILED DESCRIPTION

The embodiments of the invention provide systems and methods forfacilitating user input into an electronic system. A combination touchand transducer input system is provided, which facilitates user inputwith both ordinary objects (e.g., fingers) and transducers (e.g.,styluses) that emit an electric field for position detection.

FIG. 1 shows an exemplary tablet computer 100, suitable forincorporating a combination touch and transducer input system accordingto an embodiment of the present invention. The tablet computer 100includes a display 102, such as a LCD device, over which a generallytransparent sensing surface 104 is provided. The sensing surface 104 mayform part of the combination touch and transducer input system of thepresent invention, which is used to detect ordinary objects (e.g.,finger 106) as well as to detect one or more transducers (e.g., stylus108). Specifically, within or beneath the sensing surface 104 is anarray of electrodes (not shown in FIG. 1 ) that are configured tocapacitively sense a proximate object as well as to receive an electricfield generated by a transducer to thereby detect the position of thetransducer.

According to various exemplary embodiments of the present invention, thecombination touch and transducer input system is configured to operatein a touch sensing mode (or “touch mode” for short) and in a transducersensing mode (or “transducer mode” for short), either simultaneously orin an alternating manner by switching between the two modes insuccessive sampling periods. In the touch mode, the system is configuredto determine a position of a proximate object by capacitively sensingthe object with the array of electrodes. In the transducer mode, thesystem is configured to determine a position of a transducer bymeasuring attributes (e.g., amplitudes, phases, etc.) of a plurality ofsensing signals that are induced in the array of electrodes by anelectric field generated by the transducer. The same array of electrodesis used for both touch sensing and transducer sensing. A user can thusinterface with the tablet computer 100 with either an ordinary object(such as a finger 106) or with the transducer (such as a stylus 108).During operation, a user can thus use the finger 106 and/or the stylus108 and the sensing surface 104 to perform a variety of user interfacefunctions, such as activating icons, moving a cursor, and entering textand other data.

While the illustrated embodiment shows a tablet computer 100, theembodiments of the invention can be applied in any type of devices thatutilize an input device. Examples include other computing devices, mediadevices, and communication devices. Furthermore, while the illustratedembodiment shows a finger 106, any other capacitive object (having asize sufficient to form a mutual capacitance with at least oneelectrode) can be used for interfacing with the sensor operating in thetouch mode. Finally, while the illustrated embodiment shows a stylus108, any other suitable transducer can be used, including other pen-likedevices, pointers, cursors, pucks, mice, pawns, and other implements.

A combination touch and transducer input system generally consists of atransducer (e.g., the stylus 108 in FIG. 1 ) and a sensor 150, which isshown in FIG. 2 . The sensor 150 includes a sensor controller 152 and anarray of electrodes 154. In the illustrated embodiment, the array ofelectrodes 154 includes a first set of generally elongate electrodes 154a extending in a first (e.g., horizontal) direction, and a second set ofgenerally elongate electrodes 154 b extending in a second (e.g.,vertical) direction that is different from (e.g., perpendicular to) thefirst direction. A sheet or other geometrical arrangement of dielectricmaterial (e.g., glass, not shown) is interposed between the first andsecond sets of elongate electrodes 154 a and 154 b. Also, another sheetof material such as glass (not shown in FIG. 2 ) overlays the array ofelectrodes 154 to insulate and physically protect the array ofelectrodes 154, to collectively function as the sensing surface 104 ofFIG. 1 .

Typically, the array of electrodes 154 is formed by depositingtransparent conductive material on one or more sheets. For example, aconductor such as indium tin oxide (no) may be patterned on one side orboth sides of a glass sheet to form the first and second sets ofelongate electrodes 154 a and 154 b, respectively, over which anotherglass sheet may be applied to form the sensing surface 104. A variety ofdifferent electrode shapes (e.g., diamond-shaped electrodes andsquare-shaped electrodes) as well as array patterns may be used, and thearray of electrodes 154 for use in the present invention is not limitedto the specific configuration illustrated in FIG. 2 . For example, whileFIG. 2 shows the array of electrodes 154 formed with two layers ofoverlapping rectangular electrodes, other configurations are availablein which the first and second sets of electrodes (e.g., diamond-shapedelectrodes) do not substantially overlap with each other and thus may beprovided generally on a single layer. In various other embodiments, thefirst and second sets of electrodes do not extend substantiallyperpendicularly to each other but rather merely extend in two differentdirections. In further embodiments, the electrodes in each set need notbe substantially in parallel with each other. Still further, the arraypattern may include not only the first and second sets of electrodes,but also the third, fourth, and additional sets of electrodes that aresuitably arranged.

The controller 152 of the sensor 150 is configured to perform signalprocessing for position determination in the combination touch andtransducer input system. As will be more fully described below inreference to FIG. 5A, the sensor controller 152 suitably comprises anytype of processing device, including single integrated circuits such asa microprocessor. Additionally, the sensor controller 152 may includemultiple separate devices, including any suitable number of integratedcircuit devices and/or circuit boards working in cooperation. Forexample, the sensor controller 152 may include devices such asmicrocontrollers, processors, multiplexers, filters, amplifiers andinterfaces. Finally, in some applications the sensor controller 152 isconfigured to execute programs contained within a memory.

When operating in the touch mode, the sensor controller 152 isconfigured to determine positions of one or more proximate object(s) bycapacitively sensing each object with the array of electrodes 154.Various techniques for capacitive touch detection are known in the art,including multi-touch detection techniques capable of detecting multipletouches at a time. For example, as the sensor controller 152sequentially drives a signal to each of the first set of elongateelectrodes 154 a in the array of electrodes 154 as shown in FIG. 2 ,each intersection of the first set of elongate electrodes 154 a and thesecond set of elongate electrodes 154 b forms a capacitor. Moregenerally, each pair of at least one of the first set of elongateelectrodes 154 a and at least one of the second set of elongateelectrodes 154 b, which may or may not overlap with the at least one ofthe first set of elongate electrodes 154 a, forms a capacitor. When anobject, such as a finger, is placed on or proximate to one of thesecapacitors, a portion of the electric field lines extending from thatcapacitor is drawn toward the finger, to thereby cause a decreasingchange in capacitance of the capacitor. Such change in capacitance isreflected in a signal outputted from one of the second set of elongateelectrodes 154 b that is forming the capacitor. Thus, the controller 152can determine the position of the proximate object based on which one ofthe first set of elongate electrodes 154 a is receiving a driving signal(e.g., Y coordinate) and which one of the second set of elongateelectrodes 154 b is outputting a signal indicative of a capacitancechange (e.g., X coordinate). Again, this is one example of a capacitivetouch sensing technique, and various other techniques for capacitivetouch detection may be used in the touch mode operation of the presentinvention.

FIG. 3A is a simplified block diagram of a transducer 175 for use in acombination touch and transducer input system according to an embodimentof the present invention. The transducer 175 includes a transducercontroller 177 and an antenna 179. FIG. 3B is a partiallycross-sectional view of a transducer 175 embodied as a stylus accordingto one embodiment of the present invention. The stylus transducer 175includes a generally cylindrical elongate body 330, which houses thetransducer controller 177 (see FIG. 4 ), and an antenna 179 embodied asa pen tip of the stylus transducer 175. The transducer shown in FIG. 3Bis suitable for use in electrically (or capacitively) coupling theantenna 179 and the array of electrodes 154, using the electric fieldgenerated by the transducer 175. The following description is generallyrelated to these embodiments in which a transducer and a sensor areelectrically (or capacitively) coupled. In other embodiments of thepresent invention, however, a transducer and a sensor may bemagnetically coupled, using the magnetic field component of anelectromagnetic field generated by the transducer, as will be describedlater in reference to FIG. 11D.

The transducer controller 177 controls the operation of the transducer175 and, as will be more fully described below in reference to FIG. 4 ,may suitably comprise any type of processing device, including singleintegrated circuits such as a microprocessor. Additionally, thetransducer controller 177 may include multiple separate devices,including any suitable number of integrated circuit devices and/orcircuit boards working in cooperation. For example, the transducercontroller 177 may include devices such as pressure sensors, switches,capacitors, regulators, microcontrollers and processors.

The transducer controller 177 regulates the emitting of an electricfield from the antenna 179. When the transducer 175 is proximate thearray of electrodes 154, the electric field emitted by the antenna 179will induce sensing signals in one or more electrodes. Specifically, byapplying a voltage V to the transducer antenna 179, an amount of chargeQ is stored on the transducer antenna 179 that effectively forms a topplate of a capacitor, and an electric field is established between thetransducer antenna 179 and one or more of the array of electrodes 154that effectively form a bottom plate of the capacitor. This electricfield induces an opposing charge on the one or more of the array ofelectrodes 154, wherein the amount of charge induced is proportional tothe capacitance between the transducer antenna 179 and the one or moreelectrodes. The induced charge is independent of the frequency at whichthe voltage V is applied, and is generally expressed as below:

Q=CV  Equation (1)

where C is the capacitance between the transducer antenna 179 and theone or more electrodes on which the charge is induced. By varying thevoltage applied to the transducer antenna 179, a current can be inducedon the array of electrodes 154. Specifically, varying the appliedvoltage will change the stored charge and the electric field, therebychanging the induced charge on the array of electrodes 154. Changes inthe induced charge result in a current flow (I) in the array ofelectrodes 154, which is proportional to the applied driving frequencyas well as the voltage V and the capacitance C.

$\begin{matrix}{I = {C\frac{dV}{dt}}} & {{Equation}(2)}\end{matrix}$

According to various exemplary embodiments of the present invention, thecurrent flow, or more particularly, attributes (e.g., amplitudes,phases, etc.) of the currents (sensing signals) induced in the array ofelectrodes 154 are measured and used to determine the position of thetransducer 175. In other words, when operating in the transducer mode,the sensor controller 152 is configured to determine a position of thetransducer 175 based on the attributes of a plurality of sensing signalsthat are induced in the array of electrodes 154.

FIG. 4 is a block diagram of the transducer 175 according to oneembodiment of the invention. The transducer 175 includes a transducercontroller 177 and an antenna 179. The transducer controller 177controls the operation of the transducer 175 and may suitably compriseany type of processing device. In the illustrated embodiment, thetransducer controller 177 includes a pressure sensor 306, a powerarbitrator 308, a side switch 310, a capacitor 314 (e.g., a supercapacitor), a charge input connecter 315, a regulator 316, and amicrocontroller unit (MCU) 318. The power arbitrator 308 and the MCU 318are coupled via a general purpose input/output (GPIO) 312, and the MCU318 and the antenna 179 are coupled via another GPIO.

Referring additionally to FIG. 3B, some or all of these components ofthe transducer controller 177 and their required interfaces may bemounted on an appropriately sized circuit board 329, which is thenhoused within an appropriate transducer body 330. In the stylusimplementation shown in FIG. 3B, all components except for the capacitor314 are mounted on the board 329 inside the pen-shaped body 330. In theembodiment shown in FIG. 3B, the pressure sensor 306 is provided nearthe tip of the stylus so as to detect a pressure applied to the tipformed by the antenna 179 when the tip is applied against the sensingsurface. In other embodiments, though, the pressure sensor 306 may beplaced further away from the tip via a mechanism or linkage thattransmits the pressure information from the tip to the location of thepressure sensor 306. The side switch 310 is provided to be exposed onthe side of the pen-shaped body 330. The capacitor 314, such as a supercapacitor, is provided in the rear portion of the pen-shaped body 330,with the charge input connector 315 being exposed on the rear end of thepen-shaped body 330 to be connected to a charging docking station (notshown). The antenna 179, which functions as a pen tip for the stylustransducer 175 of FIG. 3B, may be configured of any suitable conductivematerial and may be formed in any suitable shape. In one embodiment, thestylus illustrated in FIG. 3B has a length of 120 mm and a diameter of11 mm, although the dimensions of the stylus transducer are not solimited according to the present invention.

In the illustrated embodiment, the capacitor 314 is provided to functionas a power source for the transducer 175. Any capacitor, such as a supercapacitor having a high energy density, to provide enough power tooperate the transducer 175 for a sufficient length of time may be used.For example, a 0.2 F capacitor with a rated voltage of 3.3V will be ableto provide sufficient power in most applications. As seen in FIG. 3B,the diameter of the capacitor 314 may define the diameter of thestylus-type transducer 175 and, therefore, by reducing the diameter ofthe capacitor 314, the diameter of the transducer 175 may be madesmaller to be in the range of 3-7 mm.

The capacitor 314 can be charged from a variety of sources. For example,as illustrated, it may be charged via the charge input connector 315when the transducer 175 is placed in a docking station or other storagearea of an associated device (not shown). When the transducer 175 isplaced in the docking station, power is transmitted through an ohmiccontact or from an antenna of the docking station to the transducer 175and more specifically to the capacitor 314. In another embodiment, thecapacitor 314 may be charged by receiving an electromagnetic signal fromthe array of electrodes 154 or from powering antennas providedseparately from the array of electrodes for this purpose. The poweringantenna may be located on or near the array of electrodes 154. Toreceive such an electromagnetic signal, the transducer 175 may use theantenna 179 or a separate antenna that is provided specifically for thispurpose. In these embodiments, the transducer 175 can be rechargedduring use, and therefore a smaller capacitor 314 may be used. It shouldbe noted that the capacitor 314 is one example of a power sourcesuitable for use with the transducer 175, and other types of powersources may likewise be used, such as a battery and a corded powersupply.

The pressure sensor 306 is used to detect pressure applied to thetransducer 175 and, more specifically, to the tip of the transducer incase of a stylus-form transducer. The detected pressure is then used tocontrol various operations of the transducer 175 and the combinationtouch and transducer input system. In the illustrated embodiment, thepressure sensor 306 is mounted at the tip of a pen-like transducer suchthat the pressure sensor 306 can measure the pressure at which the tipis applied to the sensing surface 104. As one example, the detectedpressure is used to “awaken” the transducer 175 from a default sleepmode. By providing a sleep mode, and awaking the transducer 175 onlywhen tip pressure is detected, the operating time of the transducer 175can be reduced to thereby conserve power. As another example, thepressure sensor 306 can be used to force the combination touch andtransducer input system to remain operating in the transducer mode aslong as a pressure value above a certain threshold is detected, insteadof switching to operating in the touch mode. As a further example, thepressure sensor 306 can be used to indicate the width or darkness of auser's stroke, such as a smaller pressure indicating a thin or lightstroke, or a larger pressure indicating a wide or dark stroke desired bythe user. A variety of different types of circuits can be used toimplement the pressure sensor 306. As one example, a variable resistorthat changes resistance as pressure is applied can be used. The changein resistance is measured and digitized by an appropriateanalog-to-digital converter (ADC), and then transmitted to the MCU 318for processing to determine the detected pressure level.

The side switch 310 is a switch that allows a user to control operationof the transducer 175, similar to the right- and left-clicking of amouse, for example. The state of the side switch 310 is passed to theMCU 318 and used in controlling the operation of the transducer 175. Forexample, it can be used to put the transducer 175 into differentoperating modes, such as in different colors or in different types ofstroke. As with the pressure information obtained by the pressure sensor306, the switch information received from the side switch 310, as wellas the transducer ID information, may be then encoded as digital data bythe MCU 318, for transmission from the antenna 179 to the array ofelectrodes 154, as will be more fully described below.

The regulator 316 provides power regulation for the transducer 175, andin particular provides a regulated power supply for the MCU 318.Especially in cordless transducer applications powered by the capacitor314 or a battery, it is desirable to minimize power consumption. Thus,the power regulator 316 preferably provides a sleep or shut-down modewith low current draw, in addition to an awake mode with regular currentdraw. In this connection, the power arbitrator 308 monitors a pressuresignal received from the pressure sensor 306 and, when the detectedpressure level exceeds a certain threshold value as determined by theMCU 318, may enable the regulator 316 to switch from the sleep mode tothe awake mode to awaken the transducer 175. Substantial power saving ispossible with awaking the transducer 175 only when sufficient tippressure is detected. A variety of different types of power regulatorscan be used, including various programmable devices with controllableoutput levels. The operation of the transducer 175 to switch between thesleep mode and the awake mode will be described below in reference toFIG. 15 .

According to some exemplary embodiments of the present invention, themicrocontroller unit (MCU) 318 carries out the overall processing forthe transducer 175 and performs generally three functions: controllingthe regulator 316 via the power arbitrator 308, providing a drivingsignal for the antenna 179, and hopping the driving signal frequency toprovide noise immunity and/or to encode digital data in the drivingsignal. In accordance with various exemplary embodiments of theinvention, the MCU 318 is a programmable device that includes an onboarddigitally controlled oscillator. The digitally controlled oscillatorprovides a driving signal for the antenna 179. The oscillator can becontrolled to provide a range of different frequencies to achievefrequency hopping and to encode digital data (e.g., pressure data,switch status data, and pen ID data) in frequency shifts of the drivingsignal for the antenna 179. In further embodiments, the MCU 318 isconfigured to encode digital data in amplitude shifts or phase shifts ofthe driving signal for the antenna 179. The MCU 318 controls the timing,durations, frequencies, amplitudes, and phases of driving signals forthe antenna 179. Therefore, the electric field generated by the antenna179 is used by the sensor 150 not only to determine a position of thetransducer 175, but also to receive and decode the digital data encodedtherein by the transducer 175. The MCU 318 preferably provides a lowpower mode which reduces operating current. The lower power mode can beused between transmission times to reduce overall power consumption. Oneexample of a microcontroller unit with low power consumption suitablefor use as the MCU 318 is a MSP430 microcontroller available from TexasInstruments.

FIG. 5A is a block diagram of the sensor 150 including the array ofelectrodes 154 and the controller 152 (see FIG. 2 ). The controller 152functions to perform signal processing for position determination of anobject (e.g., a finger) and the transducer 175, as well as for decodingdigital data encoded in the electric field generated by the transducer175. In the illustrated embodiment, the controller 152 includes ananalog multiplexer (Mux) 410, another analog multiplexer 412, aprocessing stage 414, an analog-to-digital converter (ADC) 416, and amicroprocessor unit (MPU) 420, which generally form the transducer'sposition and digital data sensing portion of the controller 152. Thecontroller 152 also includes a filter and analog-to-digital converter(ADC) 418 which together with the multiplexer 410 and the MPU 420 formthe capacitive touch sensing portion of the controller 152. One exampleof a microprocessor unit suitable for use as the MPU 420 is aprogrammable system-on-chip (PSOC) microprocessor available fromCypress. It should be noted that the configuration of the controller 152as illustrated in FIG. 5A is merely one example, and otherconfigurations of the controller 152 are possible as should be apparentto one skilled in the art. For example, the capacitive touch sensingportion and the transducer's position and digital data sensing portioncan be partially or fully combined and integrated together. In theillustrated embodiment, the MPU 420 is shared by both the capacitivesensing portion and the transducer's position and digital data sensingportion.

The multiplexer 410 selectively couples the array of electrodes 154 tothe capacitive touch sensing portion and/or to the transducer's positionand digital data sensing portion of the controller 152 depending on theoperational mode of the system. The multiplexer 410 can be implementedwith suitable analog multiplexers. These multiplexers are preferablyselected to have relatively low charge injection so as not tosignificantly disturb the capacitance of the array of electrodes 154.The multiplexer 410 is coupled to the analog multiplexer 412 in thetransducer's position and digital data sensing portion, and to thefilter and ADC 418 in the capacitive sensing portion.

In the capacitive sensing portion, the filter and ADC 418 is configuredto suitably amplify, filter, and digitize the received signals, whichthe MPU 420 processes to measure any capacitance change caused byobject(s) to thereby determine the position of the object(s). To thisend, for example, the MPU 420 may drive an electric signal to each ofthe first set of elongate electrodes 154 a, which forms a capacitor witheach of the second set of elongate electrodes 154 b, and any change incapacitance at each capacitor is monitored and measured through thecorresponding one of the second set of electrodes 154 b. The MPU 420performs the processing necessary to determine the position of theobject(s) based on the measured capacitance change. It should be notedthat a wide variety of different techniques could be used to facilitatecapacitive sensing, and the embodiments of the invention can beimplemented with any suitable capacitive sensing technique. According toone aspect of the present invention, a combination touch and transducerinput system may be advantageously constructed from any suitablecapacitive touch sensor, to which the transducer's position and digitaldata sensing function can be added.

The analog multiplexer 412 in the transducer's position and digital datasensing portion serves to connect individual electrodes in the array ofelectrodes 154 to the processing stage 414 during the transducer mode.When the electrodes are not coupled to the processing stage 414, theyare selectively terminated (e.g., grounded, terminated through aresistor to ground, or floated), as will be more fully described belowin reference to FIGS. 11B and 11C.

The processing stage 414 functions to amplify and filter the sensingsignals received from the array of electrodes 154. The processing stage414 can thus include a variety of amplifiers and filters. An example ofthe processing stage 414 will be described in detail below in referenceto FIG. 6 . The amplified and filtered signals in analog form are thenreceived by the ADC 416 and outputted therefrom in digital form to theMPU 420.

Turning to FIG. 6 , one specific embodiment of a processing stage 414 isillustrated. In this embodiment, the processing stage 414 includes anamplifier 502, an automatic gain control (AGC) 504, a notch filter 506,a bandpass filter 508 (e.g., a wideband bandpass filter), and ananti-aliasing filter 510.

The amplifier 502 amplifies the signal received from the selectedelectrode. Various types of amplifiers may be used, including a chargeamplifier, a voltage amplifier, a transimpedance amplifier, and acascoded transimpedance amplifier.

FIG. 7 illustrates an exemplary charge amplifier 600, which may be usedas the amplifier 502 of FIG. 6 . The charge amplifier 600 includes anoperational amplifier (or “op amp”) 602 set up with negative feedbackthrough a capacitor 606. The inverting input of the op amp 602 isconnected to the electrode line. The charge amplifier 600 generates avoltage proportional to the charge induced on the electrode, and thisvoltage is given by:

$\begin{matrix}{V = \frac{Q}{C}} & {{Equation}(3)}\end{matrix}$

where V is the outputted voltage, Q is the charge induced on theelectrode, and C is the feedback capacitance 606. Since any operationalamplifier suffers from input and offset bias currents at its invertingand non-inverting terminals, the charge amplifier of FIG. 7 shouldinclude a DC path for these currents to flow. For example, a resistor607 can be included in parallel with the feedback capacitor 606, tothereby create a DC path that allows the inverting terminal's biascurrents to flow without compromising the characteristics of the chargeamplifier as set by the feedback capacitor 606. This design differs fromthe transimpedance amplifier in the cascoded transimpedance amplifier ofFIG. 10 , to be described below, wherein the feedback resistor 904 issized in relation to the feedback capacitor 906 so that the impedance ofthe resistor 904 dominates in the feedback loop over the impedance ofthe capacitor 906. The appropriate values of the feedback resistors andcapacitors as used in FIGS. 7 and 10 will be readily determinable bythose skilled in the art.

FIG. 8 illustrates an exemplary voltage amplifier 700, which may be usedas the amplifier 502 of FIG. 6 . The voltage amplifier 700 includes anop amp 702 and resistors 704 and 706. The electrode line is connected tothe resistor 706.

FIG. 9 illustrates an exemplary transimpedance amplifier 800, which maybe used as the amplifier 502 of FIG. 6 . The transimpedance amplifier800 includes an op amp 802 and a resistor 804. The inverting input ofthe op amp 802 is connected to the electrode line. A current flowingthrough the feedback resistor 804 surrounding the op amp 802 isconverted to a voltage.

FIG. 10 illustrates an exemplary cascoded transimpedance amplifier 900,which may be used as the amplifier 502 of FIG. 6 . The cascodedtransimpedance amplifier 900 includes an op amp 902, a resistor 904, acapacitor 906, two constant current sources 908, 909, and a transistor,such as an NPN transistor 910. The cascoded transimpedance amplifier 900works similarly to the transimpedance amplifier 800 of FIG. 9 , in thatany current flowing through the feedback resistor 904 surrounding the opamp 902 will be converted to a voltage, as follows:

V=IR Equation (4) where V is the outputted voltage, I is the currentflowing through the feedback resistor 904, and R is the resistance ofthe feedback resistor 904. The cascoded transimpedance amplifier 900 isadvantageous in that it isolates the input capacitance of the electrodeline from the feedback resistor 904 of the transimpedance amplifier 900with the NPN transistor 910, allowing higher transimpedance gains to berealized without sacrificing bandwidth or signal to noise ratio. It alsohas improved stability by incorporating the feedback capacitor 906 inparallel with the feedback resistor 904 to control the noise gain athigher frequencies.

This combination of the transistor 910 in front of a transimpedanceamplifier is known as a cascoded transimpedance amplifier. The NPNtransistor 910 is configured as a common-base current buffer and, assuch, allows a current flowing into its emitter (E) to flow through thetransistor 910 and out to its collector (C). The current is then pickedup by the transimpedance amplifier and converted to a voltage signal.The NPN transistor emitter (E) has an equivalent small signal resistancethat is given by:

$\begin{matrix}{r = \frac{kT}{qIc}} & {{Equation}(5)}\end{matrix}$

where k is Boltzman's constant, T is temperature, q is the elementaryunit of charge, and k is the bias current flowing through the NPNtransistor. The resistance r is seen by the electrode capacitance andcreates a RC constant that can limit the bandwidth of the transimpedanceamplifier. Thus, two equal constant current sources 908, 909 areincluded in this design to establish an appropriate bias current so thatthe emitter resistance r is set small enough to allow the signal pickedup by the electrode to pass through to the transimpedance amplifier. Inanother embodiment, one constant current source may be used to achievethe same effect, although with only one current source the bias currentmay have no other way but to flow through the transimpedance amplifier.This will cause a large DC offset to be detected which, with sufficientgain, will saturate the transimpedance amplifier and wipe out thedesired signal. Using two matched constant current sources 908, 909, asillustrated, ensures that the bias current injected into the NPNtransistors 900 is also picked up and drawn away from the transimpedanceamplifier.

Returning to FIG. 6 , the amplified signal from the amplifier 502 ispassed to the automatic gain control (AGC) 504. Using feedback from theMPU 420, the AGC 504 automatically scales the output of the amplifier502. The AGC 504 is adjusted so that the dynamic range of the signaleventually fed into the ADC 416 closely matches its full scalereference. This can reduce digitization noise that could otherwiseresult when weaker signals are received by the array of electrodes 154.

The output of the AGC 504 is passed to the notch filter 506. The notchfilter 506 is provided to remove noise spikes, such as those caused bypowerline noise that is picked up by the array of electrodes 154.Suitably, a 50/60 Hz notch filter can be used to remove typical powerline noise.

The output of the notch filter 506 is passed to the bandpass filter 508,such as a wideband bandpass filter. The bandpass filter 508 is providedto pass only the selected range of predefined frequencies while blockingor removing other frequencies.

The output of the bandpass filter 508 is passed to the anti-aliasingfilter 510. The anti-aliasing filter 510 is a filter to reduce noiseabove a certain frequency to match the output signal to the ADC 416, toensure that the ADC sampling is not aliased or distorted. Theanti-aliasing filter 510 is typically implemented with a filter having avery sharp cut-off frequency.

The processing stage 414, as illustrated in FIG. 6 , thus amplifies andfilters the signals induced in and received from the array of electrodes154. Returning to FIG. 5A, the output of the processing stage 414 ispassed to the analog to digital converter (ADC) 416. The ADC 416digitizes the analog output of the processing stage 414. In oneembodiment, the ADC 416 has a sample rate of 1 million samples persecond. This provides a sufficient sampling rate to avoid aliasing whenthe transducer 175 transmits at frequencies up to 250 kHz.

The digitized output of the ADC 416 is passed to the MPU 420. The MPU420 performs the processing for determining the position of thetransducer 175 based on the received signals, as well as for decodingdigital data (e.g., pressure data, switch status data, and pen ID data)encoded in the received signals. Exemplary processes used to encodedigital data in the transducer signal, and to scan and decode thetransducer signal both to determine a position of the transducer and todecode the digital data, will be described later in reference to FIGS.11A-16 .

In various other embodiments of the present invention, the transducer175 may transmit digital data (e.g., pressure data, switch status data,and pen ID data) to the sensor 150 using other RF techniques such as viaa Bluetooth® device pursuant to IEEE 802.15 standards includingBluetooth and ZigBee protocols.

As described above, the combination touch and transducer input systemmay be configured to operate in a touch sensing mode and in a transducersensing mode in an alternating manner by switching between the two modesin successive sampling periods. To this end, the controller 152 and,more specifically the MPU 420, is configured to control the multiplexer410 so as to perform the touch sensing and transducer sensing in analternating manner. In another embodiment, the operating mode may beselected by a user of the system. For example, the sensor 150 mayinclude a switch, which the user may operate to select one of the twomodes. As another embodiment, the system operating in the transducermode may remain operating in the transducer mode as long as it isreceiving digital data from the transducer 175 indicating that a penpressure above a certain threshold value has been detected. As discussedabove, the pressure sensor 306 may be used to sense the stylus-typetransducer's tip pressure to thereby awaken the transducer only upondetecting a pen pressure exceeding a threshold value. At that time,either the pressure value, or the awake mode, may be sent from thetransducer 175 to the sensor 150. For example, the digital data may beencoded in the electric field generated by the transducer 175 andtransmitted to the sensor 150. Upon receiving (and decoding, ifnecessary) the digital data indicative of a pen pressure above athreshold value, during the transducer mode, the controller 152 mayreset its timer to automatically remain operating in the transducer modefor a predetermined amount of time, without switching to the touch mode.

Referring now to FIG. 5B, in some embodiments of the invention, thearray of electrodes 154 is divided into a touch mode section, denoted by{circle around (1)}, and a transducer mode section, denoted by {circlearound (2)}. The controller 152 is configured to simultaneously operatein the touch mode in the touch mode section {circle around (1)} and inthe transducer mode in the transducer mode section {circle around (2)}.To this end, the array of electrodes 154 needs to be suitablyreconfigured, as well as its connection with the multiplexer 410. In theillustrated embodiment, the array of electrodes 154 is divided into fourquadrants, two quadrants 422 forming the touch mode section {circlearound (1)} and the other two quadrants 424 forming the transducer modesection {circle around (2)}, at Time 1. The controller 152 may befurther configured to selectively switch the touch mode section {circlearound (1)} and the transducer mode section {circle around (2)} so thata given point on the array of electrodes 154 alternates between being inthe touch mode section and being in the transducer mode section. Forexample, in FIG. 5B, at Time 2, the touch mode section and thetransducer mode section are switched, such that the two quadrants 422that previously formed the touch mode section now form the transducermode section {circle around (2)}, while the other quadrants 424 thatpreviously formed the transducer mode section now form the touch modesection {circle around (1)}. By alternating between the state of Time 1and the state of Time 2, the controller 152 can simultaneously operateboth in the touch mode and in the transducer mode, and further, anypoint on the array of electrodes 154 alternates between being in thetouch mode section and being in the transducer mode section. While inthe illustrated embodiment the touch and transducer mode section eachconsists of two quadrants, each mode section may instead consist of onesection or of three or more sub-sections. Also, the shape of eachsection and sub-section, as well as the pattern in which multiplesections and sub-sections are combined, are not limited to what isillustrated in FIG. 5B. For example, each section or sub-section mayhave an elongate shape and be arranged generally in parallel with eachother to form stripes.

FIG. 11A is a flow chart illustrating one example of a process performedby the sensor controller 152 to scan the signals from the array ofelectrodes 154 during the transducer mode. In step 1001, themultiplexers 410, 412 are set to receive a signal from the firsthorizontal ITO line, e.g., the first Y electrode. In step 1003, theselected horizontal ITO line is scanned. In step 1005, it is determinedwhether there are more horizontal ITO lines to be scanned. If yes, instep 1006 the next horizontal ITO line is selected, and returning tostep 1003, the selected next horizontal ITO line is scanned. If in step1005 it is determined that no more horizontal ITO lines exist, in step1007, the multiplexers 410, 412 are set to receive a signal from thefirst vertical ITO line, e.g., the first X electrode. In step 1009, theselected vertical ITO line is scanned. In step 1011, it is determinedwhether there are more vertical ITO lines to be scanned. If yes, in step1013 the next vertical ITO line is selected, and returning to step 1009,the selected next vertical ITO line is scanned. If in step 1011 it isdetermined that no more vertical ITO lines exist, i.e., if it isdetermined that the entire array of electrodes 154 has been scanned,proceeding to step 1015, feedback from the scanned data is used toadjust the gain of the AGC 504 in the processing stage 414 of thecontroller 152. In accordance with various exemplary embodiments of thepresent invention, the process of FIG. 11A runs concurrently with othersoftware run by the MPU 420. This ensures that there is a constantstream of signal samples coming in from the array of electrodes 154.

Referring to FIGS. 11B and 11C, during the electrode scanning asdescribed above in reference to FIG. 11A, it has been discovered thatselectively terminating the electrodes adjacent to the electrode beingsensed improves the capacitive response of the sensed electrode tothereby produce a stable signal with improved signal-to-noise ratio.Specifically, FIG. 11B shows one of the second set of elongateelectrodes 426 being sensed, while the adjacent electrodes in the secondset of elongate electrodes 154 b are all terminated via a resistor R toground. The first set of elongate electrodes 154 a are all grounded. Asused herein, “selectively terminated” means any of the selected statesincluding being grounded (zero or low impedance), being floated (i.e.,not significantly constrained in its voltage relationship to ground,with high or infinite impedance), and being terminated via an impedanceto ground, i.e., via a resistor or another electronic device (having aselected value of impedance) to ground.

In the example of FIG. 11B, all of the adjacent electrodes in the secondset of elongate electrodes 154 b are terminated via a resistor “R,”although in other embodiments only two or more of the adjacentelectrodes may be terminated via a resistor (or floated, or grounded).For example, FIG. 11C shows another exemplary embodiment according tothe present invention, in which one of the second set of elongateelectrodes 426 is sensed, while two adjacent electrodes 427 on eitherside of the electrode 426 (total four adjacent electrodes 427) arefloated. The remaining electrodes are grounded. In this embodiment,these adjacent electrodes 427 are not coupled to ground even via anotherdevice such as a resistor. As another example, three or four adjacentelectrodes on either side of the electrode 426 may be floated, orterminated via a resistor, with the rest of the electrodes beinggrounded. Contrary to conventional wisdom that not grounding all of theadjacent electrodes will trigger cross-coupling among adjacentelectrodes, in some applications, floating or terminating via a resistorthe adjacent electrodes surprisingly improves capacitive couplingbetween the transducer 175 and the electrode being sensed 426.

In other applications, on the other hand, grounding all of the adjacentelectrodes will reduce capacitive coupling among adjacent electrodes tothereby improve the capacitive response of the electrode being sensed.This may be true, for example, when high-frequency signals are used orwhen the electrodes are very thin and have a width on the order of 1 mmand are finely spaced. A suitable manner of selective termination (e.g.,how many of the adjacent electrodes should be floated, terminated via aresister, or grounded) can be derived for a particular electrodeconfiguration pattern based on a simulation method. As a specificexample, it has been found that changing the impedance through whicheach electrode is terminated, from zero (grounded) to a certainimpedance value (through a resistor) to infinity (floated), in turncontrols the width of a signal response as illustrated in FIG. 13Bbelow. Controlling and optimizing this width will be advantageous inperforming a curve fitting procedure, also described below, to determinethe transducer's position.

While the description above generally relates to various embodiments ofthe present invention in which the transducer 175 and the sensor 150 areelectrically (capacitively) coupled based on the electric fieldgenerated by the transducer 175, in other embodiments they can bemagnetically coupled based on the magnetic field component of anelectromagnetic field generated by the transducer 175. FIG. 11Dillustrates a sample configuration of a sensor 150′ suitable for use ina magnetic coupling embodiment. In FIG. 11D, the second set of(vertical) electrodes 154 b have one side of each shorted togetherthrough a trace “Ti” while the other side of each is connected toswitches S₁-S₁₄, so that any of the second set of electrodes 154 b maybe connected to ground or to a sense line L connected to the controller152 (not shown). In the illustrated example, only one electrode 154 b′is connected to the sense line L at a time, though in other examples twoor more of the second set of electrodes 154 b or of the first set ofelectrodes 154 a may be simultaneously connected to the sense line L.While FIG. 11D shows switches S₁-S₁₄ for the second set of electrodes154 b only, it should be understood that a similar set of switches arealso connected to the first set of electrodes 154 a.

As illustrated, with switches S₃ and S₈ closed, a loop is formed that isenclosed by the second and the fourth (from the left) electrodes 154 b″and 154 b′, the section of the trace “Ti” connecting these twoelectrodes, the sense line L (to the controller 152), and a return pathP (from the controller 152) through ground that the signal must take toarrive back at the grounded electrode 154 b″. Any magnetic flux thatflows through the area enclosed by this loop will produce anelectromotive force, which can be interpreted as a current source or avoltage source connected in series with the loop. By connecting the loopto a voltage amplifier (such as the one shown in FIG. 8 ) or atransimpedance amplifier (such as those shown in FIGS. 9 and 10 ), asignal induced in the loop by a magnetic transducer can be detected.Based on the detection of such signals across a number of loops,respectively, the position of the magnetic transducer can be calculatedand determined. The magnetic transducer is configured similarly to thetransducer shown in FIG. 3B, except that it will have a loop (or coil)antenna capable of producing a stronger magnetic field as compared tothe generally pin-shaped antenna 179 of FIG. 3B.

It should be noted that, while in FIGS. 11B, 11C and 11D, the first setof electrodes 154 a are denoted as “ITO Bottom” and the second set ofelectrodes 154 b are denoted as “ITO Top,” the top and bottomorientation of the electrodes is not so limited according to the presentinvention.

As described above in reference to FIGS. 5A and 6 , the signalssequentially selected by the multiplexers 410, 412 are then amplified bythe amplifier 502, scaled by the AGC 504, filtered by the notch filter506, the bandpass filter 508, and the anti-aliasing filter 510, and thenconverted into digital values by the ADC 416. Thereafter, according tovarious exemplary embodiments of the present invention, the MPU 420 isconfigured to perform filtering of the digital values received from theADC 416. Alternatively, digital filtering may be implemented by aprocessor which is not part of MPU 420. Specifically, while the notchfilter 506, the bandpass filter 508, and the anti-aliasing filter 510substantially remove the noise, there may remain further noise thatcould be removed. Thus, the sensor controller 152 preferably uses adigital filtering technique, in the MPU 420 or in a separate processor,to remove this remaining noise from the digital values outputted fromthe ADC 416. Any suitable IIR (infinite impulse response) or FIR (finiteimpulse response) filters may be used.

Turning now to FIG. 12 , an exemplary procedure for digital filtering isillustrated. The digital filtering procedure is preferably implementedas software run by the MPU 420, though it may be implemented in anotherprocessor. In the illustrated embodiment, the digital filteringprocedure includes three channels of filtering. Each channel correspondsto one of multiple frequencies at which the electric field can begenerated by the transducer 175. In the illustrated embodiment, thetransducer 175 is configured to selectively transmit at any of threefrequencies, and thus the digital filtering procedure includes threecorresponding channels, though in other embodiments more frequencychannels may be included. Each filtering channel includes a band passfilter having a different pass frequency (F₁, F₂, F₃,), a rectificationstage, and a low pass filter. In general, the filter frequencies areselected to filter out noise from known nearby noise sources, such asthe noise from a nearby LCD screen. The output of the three band passfilters is each rectified and passed to a corresponding low pass filter.The rectification and low pass filtering of the digital values filtersout the remaining noise and extracts relevant attribute (e.g.,amplitude, phase, etc.) information from the inputted digital values.The output of the digital filtering therefore provides an accurate basisfor determining the position of the transducer 175 and for decodingdigital data encoded in the signal received from the transducer 175.

In accordance with one aspect of the invention, two or more frequencychannels are used for better noise rejection. For example, some LCDscreens radiate sharp peaks at certain frequencies. If one of thesefrequencies is the same as the frequency used by the transducer 175,other frequencies also available to the transducer 175 can be usedinstead. Thus, in accordance with one embodiment of the presentinvention, the controller 152 of the sensor 150 is further configured todetermine a signal-to-noise ratio for each of multiple frequencychannels and selects the frequency channel(s) having the highestsignal-to-noise ratio as the receiving channel(s), perhaps as part ofthe calibration process at design time. It is also possible for thecontroller 152 to then send digital data indicative of the selectedreceiving channel(s) to the transducer 175 during the transducer mode,as will be described below. The transducer 175, upon receiving anddecoding such digital data, then starts transmitting in the selectedreceiving channel(s). In accordance with another embodiment of thepresent invention, when two or more combination touch and transducerinput systems are used together (e.g., close to each other), thetransducers of those systems are configured to transmit electric fieldsat different frequencies (or at different sets of frequencies) from eachother, so as to avoid cross-coupling between the two or more systems.

As described above, the position of the transducer 175 is determinedbased on measured attributes (e.g., amplitudes, phases, etc.) of aplurality of sensing signals, which are induced in the array ofelectrodes 154 by the electric field generated by the transducer 175.For example, amplitudes of the multiple signals induced in multipleelectrodes, respectively, may be measured and compared with each otherto identify the greatest amplitude. The position of the transducer 175is determined based on the general notion that the signal having thegreatest amplitude is induced in the electrode that is closest to thetransducer 175. In other embodiments, phases of the multiple signalsinduced in multiple electrodes, respectively, may be measured andcompared with each other to determine the position of the transducer175. For example, with a 300 MHz transducer signal, the phase differencein signals induced in two electrodes that are 5 cm apart would be 18degrees. By digitizing the signals using a 600 MHz ADC, their phases canbe reconstructed. By monitoring the phase shift in each electrode, therelative movement of the transducer with respect to each electrode canbe determined. For instance, continuing with the same example, if thetransducer moves by 1 cm away from an electrode, the phase of a signalinduced in that electrode would shift by 3.6 degrees. With this method,only the relative movement of the transducer with respect to eachelectrode is known. By periodically changing the frequencies of thetransducer signal, the timing at which different electrodes sense phaseshifts can be detected and compared. The first electrode that senses aphase shift after a frequency change is the one that is closest to thetransducer. Then, by detecting subsequent phase shifts sensed in otherelectrodes, the absolute position of the transducer can be determined.Thereafter, with the same frequency, the phase shifts in differentelectrodes are monitored to determine the relative movement of thetransducer with respect to each electrode until the next frequencychange, at which time the absolute position of the transducer can bedetermined again.

According to various exemplary embodiments of the present invention, acurve-fitting technique is employed in determining the position of thetransducer 175 based on the attributes (e.g., amplitudes, phases, etc.)of the signals induced in the array of electrodes 154, which aresubsequently converted to digital values and filtered. In this regard,the MPU 420 is configured to perform a curve fitting with the digitalvalues, either within MPU 420 or in combination with one or moreprocessors, such as a main processor included in a host device (e.g., aPC that incorporates a combination touch and transducer input system ofthe invention as an input/display system). Such distributed processingmay be used in some applications when the curve-fitting processing iscomputationally intensive. In this case, the measured and filteredsignals from the array of electrodes 154 may be ported from the MPU 420to the processor in a host system for further processing, and thereafterthe resulting signals may be ported back into the MPU 420, via a serialinterface such as a selectable USB or RS232 interface (see FIG. 5A).

Any suitable parameterized curve can be used in the curve fitting. Inaccordance with various exemplary embodiments of the present invention,a suitable curve can be empirically derived for any combination touchand transducer input system including a transducer that has a particulartip (antenna) shape and an array of electrodes that has a particularelectrode configuration pattern (i.e., the shape of each electrode andthe pattern in which the array of electrodes are arranged). Thetransducer position determination based on curve-fitting is advantageousin that a suitable curve can be derived for virtually any combinationtouch and transducer input system, and also a curve derived for aparticular combination touch and transducer input system can be robustlyapplied in the same combination touch and transducer input systems thatare then mass produced. This is because the curve-fitting technique issufficiently robust to account for normal variations expected in themanufacturing processes of the systems, such as in an ITO manufacturingprocess. Because such curves can be calibrated for a wide variety ofdifferent electrode shapes and array patterns, this techniquefacilitates the use of many different shapes and configurations of thearray of electrodes, including those shapes and configurations that havebeen primarily designed for capacitive touch sensing.

FIG. 13A is a flow chart illustrating a sample process used to determinea position of the transducer based on a curve-fitting technique,according to one embodiment of the present invention. In step 1300,signal data induced in the array of electrodes 154 are collected as thetransducer 175 is placed at multiple known positions over the array ofelectrodes. In step 1302, a parameterized curve is defined that bestfits the collected signal data. These two steps may be performed atdesign time, and the defined curve is then stored in the controller 152of the sensor 150. In step 1304, during a transducer mode, signal datainduced in the array of electrodes 154 by the transducer 175 arecollected, wherein the position of the transducer is unknown to thecontroller 152. In step 1306, the position of the transducer isdetermined by fitting the data collected at step 1304 above to thedefined curve. Each of these steps will be described in detail below.

In accordance with exemplary embodiments of the present invention, twofitting curves may be derived, one for the X-position determination andthe other for the Y-position determination, though the same curve may beused for both of the X- and Y-position determinations in someapplications. For curve-fitting in each of the X and Y directions(columns and rows of the array of electrodes, respectively), theattributes (e.g., amplitudes, phases, etc.) of the signals induced in Xelectrodes and Y electrodes are established empirically ortheoretically. One experimental method of establishing the attributesinvolves scanning a transducer 175 over and across the array ofelectrodes 154 with a robotic arm or other suitable instrument. Therobotic arm may be commanded to move to a known position, with a knowntilt (e.g., during the x-position scan, an angle formed between thetransducer axis that lies in the X-Z plane and a line normal to thesensing surface), and with a known height above the sensing surface.During the X-position scan, the attributes of signals induced in the Xelectrodes are continuously recorded in an automated fashion as thetransducer is moved across and over the array of electrodes until a goodcoverage of the entire array of electrodes is achieved. Together withthe movement of the transducer in the X and Y directions, the tiltand/or height of the transducer may also be changed. For example, fortwenty (20) X electrodes, 2000 transducer positions (with tilt and/orheight) may be used to record the attributes of signals induced in the Xelectrodes. The actual number of measurements needed would typicallydepend on the symmetries in the configuration of the array of electrodes154. If symmetries exist, the measurement data recorded for a portion ofthe array of electrodes 154 may be used to infer the measurement datafor a corresponding symmetrical portion. (Step 1300 in FIG. 13A.) Asimilar process may be repeated for the Y-position scan.

Once all the measurement data for the X and Y electrodes are empiricallyor theoretically established, the data can be arranged to be a set ofmeasurement data, in which each position (and tilt/height) of thetransducer 175 is associated with the attributes of signals induced inthe X and Y electrodes by the electric field generated by the transducerat that position.

Then, the data is applied to appropriate mathematical equation(s) whichare used as the curve fitting equation(s). In other words, a curvefitting equation, or a parameterized curve, is established that fits thedata. Possible curves that can be used are polynomials, rationalpolynomials, and combinations of trigonometric, logarithmic, andexponential functions. In very simple geometries, a straight linearinterpolation may suffice. A rational polynomial may provide a goodcompromise between accuracy and speed for computation. For X electrodesthat consist of identical rectangular conductor strips, a polynomial maybe defined as follows, for example:

$\begin{matrix}{{{poly}{}(x)} = \frac{{ax^{4}} + {bx^{2}} + c}{{dx^{4}} + {ex^{2}} + f}} & {{Equation}(6)}\end{matrix}$

The above equation assumes the ith X electrode in a series of Xelectrodes as a center electrode, and looks at the expected amplitudeson that ith electrode as the transducer moves from left to right acrossthat ith electrode, wherein x represents the distance from the center ofthat ith electrode, with x<0 indicating that the transducer is to theleft of the center of the ith electrode, x>0 indicating that thetransducer is to the right of the center of the ith electrode, and x=0indicating that the transducer is at the center of the ith electrode.This rational polynomial typically has a peak at x=0 when the transduceris at the center (or right above) of the ith electrode, and theamplitude of the ith electrode decreases as the transducer moves to theleft or the right of the ith electrode. An example curve based onEquation (6) is shown in FIG. 13B. In the equation, the values for a, b,c, d, e and f are calibration parameters determined empirically for theparticular transducer tip shape and the electrode configuration patternbeing used. In this embodiment, because each electrode in the array ofelectrodes 154 is configured the same, the same curve may be generatedfor each of the X electrodes. Typically, these calibration parameterswould be defined separately for the X and Y electrodes (to therebyproduce two curves for X and Y electrodes, respectively), although thatis not required in all cases. It should be noted that Equation (6) isone example of a rational polynomial that can be used. Other polynomialsor combinations of functions may also be used. (Step 1032 in FIG. 13A.)

With the curve fitting equation (or the parameterized curve) selected,and the calibration values determined empirically, the MPU 420 is nowready to fit the incoming data to the derived curve to determine theposition of the transducer 175. This “second” curve fitting can beperformed using a variety of different techniques. For example, theposition of the transducer can be determined by minimizing the sum ofthe squares between the curve fitting equation and the measuredamplitudes, respectively. One example of this technique involves solvingthe following problem:

$\begin{matrix}{\min\left( {\sum\limits_{i = 1}^{N}{{A_{i} - {p\left( {x_{i} - x_{pen}} \right)}}}^{2}} \right)} & {{Problem}(7)}\end{matrix}$

In this example, to determine the X position of the transducer, theamplitudes induced in a series (or a plurality of) the X electrodes,such as x₁, x₂, x₃, x₄, x₅ are measured as A₁, A₂, A₃, A₄, A₅,respectively, and inputted to the problem above, where p(x) is the curvefitting equation derived above. When X electrode x₃ is selected as acenter electrode, the position of the transducer x_(pen) relative to x₃(e.g., a negative value to the left of the center of x₃ and a positivevalue to the right of the center of x₃) can be determined by solving theproblem, i.e., by determining the value x_(pen) that minimizes the sum.The process may be then repeated for another set of X electrodes, suchas for x₆, x₇, x₈, x₉, x₁₀, Similarly, the process is repeated to findthe value y_(pen), along the Y direction. By performing the curvefitting for both the X position and the Y position, the accurateposition of the transducer can be determined. (Steps 1304 and 1306 ofFIG. 13A.)

Another technique for fitting the incoming amplitude measurement data tothe predefined curve uses the greatest distance between any two points.One example of this technique entails solving the following problem:

$\begin{matrix}{\min\limits_{x_{pen}}\left\{ {\max\limits_{i}{{A_{i} - {p\left( {x_{i} - x_{pen}} \right)}}}} \right\}} & {{Problem}(8)}\end{matrix}$

This technique finds the value x_(pen) that minimizes the greatestdistance between any two points, and thus finds the best worst-case fit.This technique may be useful if a derived curve has a very flatresponse.

As further examples, techniques such as Marquardt-Levenberg andGauss-Newton can be used to quickly determine the minimum values as inProblems (7) and (8) above. These techniques typically start by using aninitial estimate for x_(pen) followed by refining the estimate using thederivatives of p(x). The process is continued iteratively, with theestimate for x_(pen) being adjusted, until little further improvement inthe minimum value is achieved. At this point, a minimum value is foundand x_(pen) is determined. Another type of curve fit algorithm uses abinary type search. In this case, a likely starting value is chosen, anda value is searched backward and forward, starting with no more than anelectrode strip difference, and sub-dividing the difference until a bestanswer is achieved. This technique may be useful whereMarquardt-Levenberg or Gauss-Newton methods are unsuited in a particularapplication. As another example, a 2D fitting simultaneously for X-Ydirections may also be used.

As described above, the attributes of signals induced in the array ofelectrodes 154 may be measured with the tilt and/or height of thetransducer being changed. Thus, a parameterized curve may be derived oradjusted, which further accounts for other data such as the tilt and/orheight of the transducer. Then, the height (or “hover”) of thetransducer above the sensing surface may be found by solving thefollowing problem, for example:

$\begin{matrix}{\min\limits_{x_{pen},h}\left( {\sum\limits_{i = 1}^{7}{{A_{i} - {h*{p\left( {x_{i} - x_{pen}} \right)}}}}^{2}} \right)} & {{Problem}(9)}\end{matrix}$

In this example, seven X electrodes are used (with x₄ as a centerelectrode), with amplitude Ai detected in the ith electrode, and h isthe height. The X position of the transducer x_(pen) relative to x₄ andthe height h are found by determining the values x_(pen) and h thatminimize the sum. In the problem above, note that the signal strengthdecreases proportionally to 1/h, as the transducer moves away from thesensing surface.

In another example, the tilt of the transducer may be parameterized interms of the following equation including trigonometric functions, whichis suitable for use in a magnetic coupling embodiment:

$\begin{matrix}{P = {❘{\frac{\sin\left( {p_{tilt} + {\tan^{- 1}\left( \frac{x_{i} - W_{ito}}{h} \right)}} \right)}{\sqrt{\left( {\left( {x_{i} - W_{ito}} \right)^{2} + h^{2}} \right)}} - \frac{\sin\left( {p_{tilt} + {\tan^{- 1}\left( \frac{x_{i} + W_{ito}}{h} \right)}} \right)}{\sqrt{\left( {\left( {x_{i} + W_{ito}} \right)^{2} + h^{2}} \right)}}}❘}} & {{Equation}(10)}\end{matrix}$

where P_(tilt) is the tilt angle relative to the axis perpendicular tothe sensing surface in the X direction, and W_(ito) is the width of oneelectrode loop.

In another variation on this technique, the curve fitting can beweighted to increase accuracy. Typically this is done by weightingstronger signals a greater amount, as the stronger signals typicallyhave a higher signal to noise ratio. In some cases, it may be desirableto start with an initial estimate for x_(pen) at the center of thestrongest-signal electrode. This improves the probability that theactual minimum will be found by a search algorithm.

As used herein, and as supported by the description above, the term“curve fitting” or “fitting” refers to one or more of a wide range oftechniques used to construct one or more curves that best fit “test”data and to subsequently use the one or more curves to process “actual”data. Various examples are disclosed, in which a defined curve is fittedto actual data by minimizing error (e.g., the sum of the squares)between the curve and the actual data, or in which the curve is fittedthrough an iterative process. In other examples, however, anon-iterative process may be used, For example, with least squareslinear regression, a good fit can be obtained without iteration andwithout having to minimize error. It is also possible to sacrifice somepositioning data in exchange for a faster algorithm. For example, withcertain arrays of electrodes having linear electrodes with good signalto noise ratio, a simple linear interpolation method can be used betweentwo electrodes with the highest amplitudes, to thereby determine theposition of the transducer.

As described above, according to various exemplary embodiments of thepresent invention, the transducer controller 177 selectively generatesan electric field at multiple frequencies and, more specifically, atsequentially different frequencies using a frequency hopping technique.Specifically, in various embodiments of the present invention, the MCU318 in the transducer controller 177 includes an onboard digitallycontrolled oscillator that is configured to selectively generate anantenna driving signal at a range of different frequencies. Hopping fromone frequency to another in driving the antenna 179 correspondinglychanges the frequency of the electric field generated by the antenna179, to achieve improved noise rejection. Furthermore, these differentfrequencies can be used to encode and send digital data from thetransducer 175 to the array of electrodes 154 and hence to the sensorcontroller 152. For example, suitable Frequency-Shift Keying (FSK)techniques can be used to encode and transmit digital data regarding thetransducer, such as pressure data, switch status data, and transducer IDdata. The transducer ID data may be useful for the sensor 150 touniquely identify a particular transducer. For example, when the sensor150 is used in a point-of-sale system and different sales agents carrydifferent transducers, the sensor can automatically identify aparticular sales agent inputting data based on the transducer ID datareceived from the agent's transducer. As another example, when aplurality of combination touch and transducer input systems inaccordance with the present invention are used close to each other, itwould be desirable for each sensor to uniquely identify itscorresponding transducer (while discriminating against othertransducers) so as to process only the signal received from thecorresponding transducer.

In accordance with one aspect of the invention, the frequencies used incommunication between the transducer 175 and the sensor 150 may bedefined by dividing down a known (base) frequency. This method providesan advantage of avoiding harmonics of a base frequency and providingbetter noise rejection. In one example, the transducer 175 operates intwo modes. The first mode is a low power mode, which can generate fourfrequencies. The second mode is a high power mode, which consumes morepower than the low power mode, but provides a larger number offrequencies that are not harmonics of the base frequency. Table 1 belowshows the possible frequencies that could be used by the transduceraccording to one embodiment of the invention.

TABLE 1 500 KHz Base 2 MHz Base Frequency (Low Power) Frequency (HighPower) Pen Transmit Pen Transmit Divisor Frequency (KHz) DivisorFrequency (KHz) 2 250  8 250  9 222 10 200 11 182 3 166 12 166 13 154 14143 15 133 4 125 16 125 17 118 18 111 19 105 5 100 20 100In both the low power mode and the high power mode, usable frequenciesare determined by dividing down a base frequency (500 KHz and 2 MHz,respectively). It should be noted that Table 1 above shows merely oneexample of a set of different frequencies that are usable according toone embodiment of the invention, and other sets of different frequenciesmay be selected for use in accordance with other embodiments of theinvention. Various other methods may be used to select a set ofdifferent suitable frequencies, such as a method using Phased LockedLoops (PLLs).

Construction of a PLL is well known in the art. A sample PLL suitablefor use pursuant to an embodiment of the present invention is shown inFIG. 13C, which includes a reference frequency (RO 1310, a VoltageControlled Oscillator (VCO) 1312, a phase detector 1314, and a loopfilter consisting of an operational amplifier 1316 and two resistors1318 a and 1318 b. To generate different frequencies from the referencefrequency (RI), the PLL includes one or more frequency dividers (“M”divider 1320 and “N” divider 1322 in the illustrated embodiment). Theillustrated PLL can generate frequencies of the form M/N based on thereference frequency (RI). This allows a vast range of frequencies to becreated, which share a base frequency that is a fraction of a hertz. Forexample, if N can range from 1 to 16, one may select 16, 15, 13, and 11as the divisors in the “N” divider 1322. If 11 or 7 is selected as thedivisor in the “M” divider 1320, and the reference frequency (RI) is 500KHz, the following output frequencies could be generated:

11/16*500 KHz=343.75 KHz

11/15*500 KHz=366.67 KHz

11/13*500 KHz=423.08 KHz

7/11*500 KHz=318.18 KHz

These frequencies all share a fundamental frequency of less than ¼ of ahertz. The PLL can advantageously generate a range of frequencies thatare closer together with little similar harmonic content. This allowsfor the use of narrower bandpass filters (508) in the analog processingstage 414 of the sensor controller 152, thereby increasing the signal tonoise ratio before the digitization of the signal.

In one embodiment, the transducer 175 is configured to generate fourdifferent frequencies within a specified range (e.g., 100 kHz, 125 kHz,166 kHz, and 250 kHz as in the “low power” mode in Table 1 above). Thetransducer controller 177 is configured to switch between these fourdifferent frequencies as needed for noise rejection or to encode digitaldata in frequency shifts. A variety of techniques can be used to encodedigital data using frequency hopping, and any suitable Frequency-ShiftKeying (FSK) technique may be used. Additionally or alternatively, anysuitable Amplitude-Shift Keying (ASK) technique, Phase-Shift Keying(PSK) technique, or more complicated encoding schemes such as QuadratureAmplitude Modulation (QAM) scheme may be used to encode digital data.

As one specific example, Manchester type code may be used to encodedigital data, wherein a transition of frequencies from high to lowtransmits a “1,” while a transition of frequencies from low to hightransmits a “0.” Table 2 below illustrates a sample data encoding schemebased on Manchester type code.

TABLE 2 Encoding Meaning 111 Start of frame (SOF) 001 Send a 0 011 Senda 1 000 End of frame (EOF)

As shown above, three successive transitions of high to low (“111”)indicate a start of frame (SOF), and three successive transitions of lowto high (“000”) indicate an end of frame (EOF). In between the SOF andEOF, any three transitions of “001” sends a “0” and any threetransitions of “011” sends a “1.” These digital data (SOF, 0, 1, andEOF) are transmitted in data frames, an example of which is shown inFIG. 14 . The data frame as shown in FIG. 14 has a unique start bitsequence (SOF) and end bit sequence (EOF) and, therefore, can havedifferent lengths. The data frame of FIG. 14 includes a start of frame(SOF) block 950, followed by a data type block 952 (2 bits), a payloaddata block 954 (3-24 bits), and finally by an end of frame (EOF) block956. Table 3 below shows one example of data frame formats for each typeof data.

TABLE 3 Data Length Data Type Value (bits) Comments Pen ID 00 24 Enoughfor 16 million unique factory-programmed pen ID's Switch 01 3 Canprovide for 3 switches, each with two or more states (e.g., ON/OFF)Pressure 10 8 Up to 256 pressure values

In the above example, 2 bits of “00” indicate “pen ID” data, to befollowed by 24 bits indicating a unique pen ID number. 2 bits of “01”indicate “switch status” data, to be followed by 3 bits indicating astatus of one of up to three switches. Finally, 2 bits of “10” indicate“pressure” data, to be followed by 8 bits indicating the detectedpressure value. Though only three types of data are shown above, more ordifferent types of data may be defined to be digitally encoded. Forexample, data derived from any other sensors provided on the transducer175, such as a tilt sensor or a rotational sensor, or the operating modeof the transducer 175 (e.g., “awake mode” or “sleep mode”) may bedefined and digitally encoded.

Table 4 below shows one example of a data frame containing switch statusdata.

TABLE 4 SOF 0 1 1 0 0 EOF 1 1 1 0 0 1 0 1 1 0 1 1 0 0 1 0 0 1 0 0 0In the example above, first, three successive frequency transitions ofhigh to low (“111”) indicate a start of frame (SOF). The next 2 bits of“01” are generated by the frequency transitions of “001” and “011” andindicate that this data frame includes “switch status” data and that thepayload data are 3-bits long. The following 3 bits of “100” aregenerated by the frequency transitions of “011,” “001” and “001,”respectively, and indicate that a first switch is pressed. Lastly, thethree successive frequency transitions of low to high (“000”) indicatean end of frame (EOF).

The rate of data transmission provided by the methods described abovewould depend upon the rate of frequency hopping. For example, if thefrequency hopping can be made to occur every 250 μs, with four possiblefrequencies, the system can transmit a throughput of 1000 bits persecond.

The present invention is not limited to the particular examplesdescribed above, and various other digital encoding or modulationtechniques may be used as well as other data frame formats. For example,other encoding techniques with advanced features such as errorcorrection may be used (e.g., Reed-Solomon coding technique).

FIG. 15 is a flow chart illustrating an exemplary process to beperformed generally by the transducer controller 177, and morespecifically by the MCU 318 thereof, including the process of encodingand transmitting digital data to the sensor 150, according to oneembodiment of the invention. After the transducer “wakes up,” in step1060, a timer is set to go to “sleep.” Once the timer is set to “sleep”and a certain amount of time elapses, i.e., when the timer expires, thetransducer goes to “sleep.” In step 1062, the pen tip pressure is readfrom the pressure sensor 306. In step 1064, it is determined whether thepen tip pressure detected in step 1062 is above a threshold value. Ifyes, proceeding to step 1066, the timer is reset to go to “sleep.” Then,in step 1068, the pen tip pressure is encoded as digital data andtransmitted to the sensor 150. Likewise, in step 1070, the side switchstatus is encoded as digital data and transmitted to the sensor 150. Instep 1072, it is determined whether the side switch status has beenchanged. If yes, in step 1074, the timer is reset to go to “sleep.”Then, in step 1076, pen ID information is encoded as digital data andtransmitted to the sensor 150. In step 1078, it is determined whetherthe timer has expired. If not (for example, due to the timer having beenreset in steps 1066 and 1074), the process returns to step 1062, and thepen tip pressure is read again and the process repeats itself. If, onthe other hand, it is determined in step 1078 that the timer hasexpired, it proceeds to step 1080 and the transducer goes to “sleep.”Thus, the transducer wakes up (and resets the “sleep” timer) whenever aninterrupt is generated. An interrupt is generated when the detected pentip pressure exceeds a threshold value (step 1064) or when the sideswitch status has been changed (step 1072).

FIG. 16 is a flow chart illustrating an exemplary process to beperformed generally by the sensor controller 152 for decoding digitaldata encoded in frequency shifts of a signal generated by the transducer175. In step 1020, a pen frequency state is set to “unknown.” In step1022, it is determined whether a pen frequency has been detected. Ifyes, in step 1024, it is determined whether the pen frequency state is“unknown.” Specifically, in this example, there may be ten frequencystates that are predefined. If the frequency detected in step 1022 isnot any of the “known” frequency states, then proceeding to step 1026,it is marked that the frequency-moving direction (is unknown and thus)needs to be searched, and thereafter returning to step 1022 it isdetermined whether a pen frequency has been detected. If in step 1024 itis determined that the pen frequency detected in step 1022 is one of the“known” frequency states, then proceeding to step 1028, it is determinedwhether the frequency has changed since the last detection. If no, againreturning to step 1022, it is determined whether a pen frequency hasbeen detected.

If, in step 1028, it is determined that the frequency has changed sincethe last detection, proceeding to step 1030, it is determined whetherthe frequency-moving direction needs to be searched. Initially, thefrequency-moving direction is unknown and thus needs to be searched.Therefore, proceeding to step 1032, it is determined whether thepresently-detected frequency is lower than the last-detected frequency.If yes, proceeding to step 1034, it is marked that the frequency isgoing “high to low,” while if no, proceeding to step 1036, it is markedthat the frequency is going “low to high.” From either of steps 1034 and1036, returning to step 1022, it is again determined whether a penfrequency has been detected (“yes” in this case coming from either ofsteps 1034 and 1036). Proceeding down to step 1028, if it is determinedthat the frequency has changed since the last detection (“yes” in thiscase coming from either of steps 1034 and 1036), in step 1030, it isdetermined whether the frequency-moving direction needs to be searched.At this time, the frequency-moving direction has already been marked aseither “high to low” (in step 1034) or “low to high” (in step 1036).Thus, the frequency-moving direction need not be searched, andproceeding to step 1038, it is determined whether the presently-detectedfrequency has moved from the last-detected frequency in the samedirection as the frequency-moving direction as previously marked insteps 1034 or 1036. If yes, proceeding to step 1040, “1” is recorded ifthe frequency-moving direction is “high to low” and “0” is recorded ifthe frequency-moving direction is “low to high.”

Thereafter, proceeding to step 1042, it is determined whether thepresently-detected frequency is greater than a predefined threshold,such as 143 kHz in the illustrated embodiment. The threshold ispredefined generally near a middle point in the range of predefinedfrequencies (e.g., 143 kHz, within the range expanding from 100 kHz to250 kHz in the illustrated embodiment). If the presently-detectedfrequency is greater than the predefined threshold, in step 1044 it ismarked that the frequency-moving direction is “high to low,” while ifthe presently-detected frequency is equal to or less than the predefinedthreshold, in step 1046 it is marked that the frequency-moving directionis “low to high.” From either of steps 1044 and 1046, returning to step1022, it is again determined whether a pen frequency has been detected.If not, proceeding to step 1048, it is determined whether more than apredefined amount of time has elapsed since the last detection of afrequency. If so, proceeding to step 1050, a start of a new word (or anew data frame) is indicated.

In some embodiments of the present invention, digital encoding andcommunication using frequency hopping is achieved bi-directionallybetween the transducer 175 and the sensor 150. Digital data can beencoded in a similar manner by the sensor 150 and transmitted to thetransducer 175. The types of data that are digitally encoded by thesensor 150 may include, for example, sensor ID data, receiving channeldata (i.e., which frequency channels should be used), and the operatingmode of the sensor 150. Further additionally or alternatively, digitaldata regarding pressure, switch status, pen ID and others, may betransmitted between the transducer 175 and the sensor 150 using other RFtechniques such as via a Bluetooth® device pursuant to IEEE 802.15standards including Bluetooth and ZigBee protocols.

According to one aspect of the invention, a cordless transducer 175 isprovided, which is configured for use with an array of electrodes 154,wherein the cordless transducer 175 and the array of electrodes 154 arecapacitively coupled. The cordless transducer 175 includes a pen-shapedhousing (330 in FIG. 3B) including a pen tip (179 in FIG. 3B) at itsdistal end, and a transducer controller 177 arranged within thepen-shaped housing 330. The transducer controller 177 controls theoperation of the cordless transducer 175, and includes a pressure sensor306 for detecting the pressure applied to the pen tip. The cordlesstransducer 175 also includes an antenna 179 coupled to the transducercontroller 177 to transmit the pressure sensor data, which is detectedby the pressure sensor 306, as digital data to the array of electrodes154. The transducer controller 177 includes a power storage device, suchas a battery or a capacitor (314), which supplies power to drive thetransducer controller 177 and the antenna 179, to thereby achieve thecordless transducer.

The cordless transducer 175, described above, may be provided with asuitable sensor 150 to together form a combination touch and transducerinput system. In some embodiments, the combination touch and transducerinput system may further include a docking (charging) station, suitablyformed to receive the cordless transducer 175 therein to charge thecapacitor (314 in FIG. 4 ) via the charge input connector 315.

According to a further aspect of the invention, a method is provided forselectively determining a position of a proximate object and a positionof a transducer. The method includes eight steps. First, the proximateobject is capacitively sensed with an array of electrodes 154. Second, aposition of the proximate object is determined based on the capacitivesensing. Third, an electric field is generated with the transducer 175.Fourth, digital data is transmitted from the transducer 175. Fifth, aplurality of sensing signals are induced based on the electric field ina corresponding plurality of electrodes in the array of electrodes 154.Sixth, attributes of the plurality of sensing signals are measured.Seventh, a position of the transducer 175 is determined based on themeasured attributes of the plurality of sensing signals. Eighth, thedigital data is received with the array of electrodes 154.

According to one aspect of the invention, the transducer 175 and thesensor 150 can communicate asynchronously for the purpose of bothtransducer position determination and digital data communication.Specifically, because the systems and methods of the present inventionaccording to some embodiments rely on determining the amplitude andfrequencies of the signals induced in the electrodes, it does notrequire a specific phase correlation between the transducer 175 and thesensor 150. This has many potential advantages. For example, it does notrequire the use of a wired or dedicated wireless link for syncing.Dedicated wireless links for syncing can require a bulky transmitter onthe part of the sensor 150. Furthermore, the dedicated wireless linksfor syncing could provide a possible source of interference with otherdevices, and also are more likely to be interfered with by otherdevices. Additionally, the asynchronous design achievable with thepresent invention facilitates the use of different frequencies betweenthe transducer 175 and the sensor 150. Asynchronous designs are alsoless likely to degrade over time, and are more likely to be compatiblewith a wide range of devices.

The embodiments and examples set forth herein were presented in order todescribe the present invention and its particular application and tothereby enable those skilled in the art to make and use the invention.However, those skilled in the art will recognize that the foregoingdescription and examples have been presented for the purposes ofillustration and example only. The description as set forth is notintended to be exhaustive or to limit the invention to the precise formdisclosed. Many modifications and variations are possible in light ofthe above teaching without departing from the spirit of the forthcomingclaims.

1. A combination touch and transducer input system, comprising: atransducer configured to generate an electric field; an array ofelectrodes; and a controller coupled to the array of electrodes, thecontroller being configured to: when operating in a touch mode,determine a position of a proximate object by capacitively sensing theobject with the array of electrodes; and when operating in a transducermode, determine a position of the transducer by measuring attributes ofa plurality of sensing signals, the plurality of sensing signals beinginduced in the array of electrodes by the electric field generated bythe transducer; wherein the transducer is configured to transmit digitaldata to the array of electrodes by modulating a signal of a frequencyselected among multiple frequencies by dividing down a known basefrequency, and the controller is configured to receive the digital datavia the array of electrodes.
 2. The system of claim 1, wherein thetransducer is configured to selectively generate the electric field atthe multiple frequencies and the controller is further configured toselect one of multiple channels of the multiple frequencies as areceiving channel.
 3. The system of claim 1, wherein communicationbetween the transducer and the controller is bi-directional and datatransmitted from the controller to the transducer includes a receivingchannel data indicating which frequency channels should be used by thetransducer.
 4. The system of claim 1, wherein the transducer compriseselectronic circuitry configured to selectively generate the electricfield at the multiple frequencies and to encode the digital data infrequency shifts of the generated field, and the controller isconfigured to detect the plurality of sensing signals at the multiplefrequencies and to decode the digital data encoded in the frequencyshifts.
 5. The system of claim 1, wherein the digital data includes oneor more of a pressure data, switch status data, and transduceridentification data.
 6. The system of claim 1, wherein the transducercomprises electronic circuitry configured to encode the digital data inphase shifts or amplitude shifts of the generated electric field.
 7. Thesystem of claim 1, wherein the transducer and the controller communicateasynchronously.
 8. The system of claim 1, wherein the controllerdetermines a signal-to-noise ratio for each frequency channel andselects the frequency channel having the highest signal-to-noise ratioas the receiving channel.
 9. The system of claim 1, wherein thecontroller is further configured to transmit digital data to thetransducer, and the transducer is configured to receive the digitaldata.
 10. The system of claim 1, wherein a second combination touch andtransducer input system is provided, comprising a second transducer, asecond array of electrodes, and a second controller, the secondtransducer being configured to generate an electric field at a secondset of one or more frequencies different from the multiple frequenciesand the second controller being configured to detect the generatedelected field at the second set of one or more frequencies.
 11. Thesystem of claim 1, wherein the controller is further configured todetermine the position of the transducer by fitting at least some of themeasured attributes of the plurality of sensing signals to apre-determined parameterized curve.
 12. The system of claim 1, whereinthe array of electrodes comprises: a first set of elongate electrodesarranged substantially in parallel with each other and extending in afirst direction; and a second set of elongate electrodes arrangedsubstantially in parallel with each other and extending in a seconddirection that is different from the first direction; wherein each pairof at least one of the first set of elongate electrodes and at least oneof the second set of elongate electrodes forms a capacitor; wherein thetransducer and the array of electrodes are electrically coupled; andwherein the controller is further configured to: when operating in thetouch mode, supply a signal to each of the first set of elongateelectrodes, detect a capacitance change reflected in a signal outputtedfrom each of the second set of elongate electrodes, and determine theposition of the proximate object based on the detected capacitancechange; and when operating in the transducer mode, measure attributes ofa plurality of sensing signals outputted from the first and second setsof elongate electrodes and calculate the position of the transducerbased on the measured attributes.
 13. The system of claim 12, whereinthe controller is further configured to, when operating in thetransducer mode: measure an attribute of a sensing signal outputted fromeach of the first set of elongate electrodes while selectivelyterminating two or more of the first set of elongate electrodes that areadjacent to the elongate electrode being sensed, and measure anattribute of a sensing signal outputted from each of the second set ofelongate electrodes while selectively terminating two or more of thesecond set of elongate electrodes that are adjacent to the elongateelectrode being sensed.
 14. The system of claim 13, wherein the two ormore of the first set of elongate electrodes that are adjacent to theelongate electrode being sensed are grounded, and the two or more of thesecond set of elongate electrodes that are adjacent to the elongateelectrode being sensed are grounded.
 15. The system of claim 13, whereinthe two or more of the first set of elongate electrodes that areadjacent to the elongate electrode being sensed are floated, and the twoor more of the second set of elongate electrodes that are adjacent tothe elongate electrode being sensed are floated.
 16. The system of claim13, wherein the two or more of the first set of elongate electrodes thatare adjacent to the elongate electrode being sensed are terminated viaan impedance to ground, and the two or more of the second set ofelongate electrodes that are adjacent to the elongate electrode beingsensed are terminated via an impedance to ground.
 17. The system ofclaim 1, wherein the controller is configured to alternate betweenoperating in the touch mode and operating in the transducer mode insuccessive sampling periods of the system.
 18. The system of claim 1,wherein the controller is configured to selectively divide the array ofelectrodes into a touch mode section and a transducer mode section, andto simultaneously operate in the touch mode in the touch mode sectionand in the transducer mode in the transducer mode section.
 19. Thesystem of claim 1, wherein the controller includes an amplifier selectedfrom a group consisting of a charge amplifier, a voltage amplifier, atransimpedance amplifier, and a cascoded transimpedance amplifier, eachbeing coupled to the array of electrodes and configured to amplify theplurality of sensing signals induced by the electric field in the arrayof electrodes.
 20. The system of claim 1, wherein the transducerincludes a capacitor or a battery configured to function as a powersource for the transducer.